Spriggans seem to be to Kyne what dragons are to Akatosh, I guess. Creation of Kynareth.
The Spriggans also protect the Eldergleam, so they serve not only the Kynareth-aspect, but the Kyne-aspect. I wouldn't be at all surprised to hear that they can be found in High Rock, too.
I'm pretty sure you can find them wherever there is an "abundance" of "nature".
They're nature's guardians. They apparently protect secluded places sacred to Kynareth, including the groves where special trees bloom and where animals live peacefully. A pair of them stood near the Boots of the Crusader as well, but they were non hostile because to even see them the worthy knight had to pass Nature's test.
Though I doubt that there are any or many in Valenwood, as the Bosmer serve their core purpose.
Valenwood doesn't need spriggans...they've got bad, bad things left over from the Wild Hunts.
Ever tangled with a Jabberwock? You don't want to.